Hello, welcome to the forum.
Rules for skin-making can be found here in case you haven’t seen it.
Be sure to have the proper dimensions for the skin (300x300) and the sword (260x280)
I will say that the bar for skins making it into the game is set very high. Yours might not be detailed enough to be accepted, since it is rather simplistic compared to a lot of the skins that have made it into the game. With that said, don’t let that discourage you; keep trying and looking for improvement.
A bit of feedback: Adding a bit of shading/giving the moon a bit of a shadow might help.